1. Field of the Invention
The present invention relates to a playback process in a disk drive apparatus and particularly to a disk drive apparatus, a disk playback method, and a disk adapted in which when the disk action is shifted from a not recorded area to a recorded area of a disk medium, its readout signal is subjected to a filtering process for minimizing the unstable period thereof.
2. Description of the Related Art
Typical recording media and record/playback apparatuses capable of recording and playing back of digital data include optical disks such as a digital versatile disk (DVD). For example, a DVD-RAM, one type of DVD, has a signal recording layer provided in its recording medium where the crystalline condition of the recording layer is modified by irradiating the signal recording layer with a laser beam having a proper energy. When irradiating the signal recording layer with a laser beam having a proper energy again, a reflected light of an amount according to the crystalline condition of the recording layer is obtained. Digital data is recorded and reproduced by detecting the reflected light. Other similar type of optical disk like DVD-RW and a DVD-R are commercially available. Also, optical disk drives employing the shorter wavelength of blue laser light have been introduced in the market. These recording media are substantially equal in the size but quite different in the detailed factors.
The signal recording layer of the recording medium has various conditions. For example, the recording layer of the optical disk consists mainly of a series of non-laser-irradiated regions (non-recorded areas) and laser-irradiated regions (recorded areas) along a track. Also, the optical disk may has a series of pits between the common recording areas.
It is not unusual during the playback operation that the DC level in the reflected light remains not stable due to the condition of the medium. If the DC level of the reflected light is significantly changed, it may cause malfunctions of the circuitry components at the subsequent stage. For compensation, some prior arts of improvement have been proposed.
In Jpn. Pat. Appln. KOKAI Publication No. 2000-182239, one of the related arts is disclosed in which the cut-off frequency of a highpass filter (HPF) is temporarily switched to another for shortening the length of the transient response.
In Jpn. Pat. Appln. KOKAI Publication No. 2000-331425, another related art is disclosed in which the cutoff frequency of a highpass filter (HPF) is temporarily increased to a high level and then decreased by small steps.
It is yet troublesome in the related art of Jpn. Pat. Appln. KOKAI Publication No. 2000-182239 that when the playback action is shifted from the non-recorded area to the recorded area, the transient response in the output signal is again attenuated to zero at one of the two cutoff frequencies but not by the other cutoff frequency immediately after the switching and may cause the downstream circuits to be functioned with difficulty.
The related art of Jpn. Pat. Appln. KOKAI Publication No. 2000-331425 also fails to eliminate completely the transient response when the playback action is varied in the speed or conducted in different formats because the sequence (speed) of declining the cutoff frequency is fixed, although the level of the transient response remains low with the cutoff frequency being declined gradually.
In addition, a further related art is disclosed for reference as Jpn. Pat. Appln. KOKAI Publication No. 2003-157528.